Microenvironmental Regulation of Telomerase Isoforms in Human Embryonic Stem Cells

Recent evidence points to extra-telomeric, non-canonical roles for telomerase in regulating stem cell function. In this study, human embryonic stem cells (hESCs) were cultured in 20% or 2% oxygen microenvironments for up to five days and evaluated for telomerase reverse transcriptase (TERT) expression and telomerase activity. Results showed increased cell survival and maintenance of the undifferentiated state with elevated levels of nuclear TERT in 2% oxygen cultured hESCs despite no significant difference in telomerase activity compared to their high oxygen cultured counterparts. Pharmacological inhibition of telomerase activity using a synthetic tea catechin resulted in spontaneous hESC differentiation, while telomerase inhibition with a phosphorothioate oligonucleotide telomere mimic did not. RT-PCR analysis revealed variations in transcript levels of full-length and alternate splice variants of TERT in hESCs cultured under varying oxygen atmospheres. Steric-blocking of Δα and Δβ hTERT splicing using Morpholino oligonucleotides altered the hTERT splicing pattern and rapidly induced spontaneous hESC differentiation that appeared biased toward endomesodermal and neuroectodermal cell fates, respectively. Together, these results suggest that post-transcriptional regulation of TERT under varying oxygen microenvironments may help regulate hESC survival, self-renewal and differentiation capabilities through expression of extra-telomeric telomerase isoforms.